Abstract: Water penetration into HPMC matrices may be observed when they are brought into contact with water. The effects of HPMC substitute type on the water penetration are concentrated on the initially short time, which is considered to be the time for HPMC to form a hydrogel. After hydrogel is formed, the water penetration rate is identical. The effect of HPMC on water penetration depends on its molecular weight. When a drug is added into HPMC matrix, the ability of water penetration into matrix is weakened. As the water penetrates, a considerable swelling of the HPMC matrix is also observed, axial swelling is greater than radial swelling, and the swelling of matrix is mainly produced by HPMC. High HPMC level produces large swelling of matrix. Linear relations exist between water penetration, matrix swelling and drug release.

Key words: Hydroxypropylmethyl cellulose, Hydroxypropylmethyl cellulose, Drug release, Drug release, Water penetration, Water penetration, Matrix expansion, Matrix expansion